Regarding Bitmap Scan

From: "soni de" <soni(dot)de(at)gmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Regarding Bitmap Scan
Date: 2006-10-17 11:39:29
Message-ID: 9f2e40a90610170439n4b670c23ld586e4f0840e943@mail.gmail.com
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Hello,

I was going through the Performance Enhancements of 8.1.0, in that I have
read "Bitmap Scan"

"*Bitmap Scan:* indexes will be dynamically converted to bitmaps in memory
when appropriate, giving up to twenty times faster index performance on
complex queries against very large tables. This also helps simplify database
management by greatly reducing the need for multi-column indexes."

I didn't understand the "Bitmap Scan" and the sentence "indexes will be
dynamically converted to bitmaps in memory". What does mean by "Bitmap Scan"
in database?

Can anybody help us regarding above query?

Thanks,

Soni

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